The present invention relates to electronic still cameras with strobo capable of continuously emitting light.
With the recent spread of personal computers, electronic still cameras have been widely used, with which a CCD or like solid-state imaging element is used in lieu of silver salt film for picking up an optical image of a scene and directly obtaining electronic data of the picked-up image.
In this type of electronic still cameras, the solid-state imaging element has narrow latitude (i.e., dynamic range) compared to the silver salt film and also it is possible to make ready sensitivity adjustment by adjusting the gain of an amplifier which amplifies the electric signal of the image obtained by the solid-state imaging element. An increase in accuracy of the exposure control inclusive of the amplifier gain adjustment has been desired.
Cameras of this type include one, in which, when carrying out strobo photographing, prior to the regular photographing, preliminarily strobo light emission (hereinafter referred to as preliminary light emission) is caused in correspondence with shutter release button operation to detect the intensity of light reflected from the scene and check if the intensity of light emitted from the strobo is sufficient and, when it is decided that the strobo light intensity is insufficient, the gain of the amplifier is adjusted (i.e., the photographing sensitivity is increased) in such a manner as to make up for the insufficient light intensity before making the regular photographing by causing strobo light emission.
The operation described above is carried out in order to obtain an accurate exposure level (i.e., brightness of the picked-up image) in the photographing accompanied by the strobo light emission. At the time of increasing the photographing sensitivity as described above, the photographing sensitivity is determined without taking the exposure level, which has been determined in an AE (automatic exposure) process without strobo light emission right before the photographing, into consideration at all.
In this case, when the amplifier gain is increased to meet the main foreground subject of scene, which is located at a position relatively close to the camera and in a strobo photographing range, proper exposure level can be obtained with respect to the main foreground subject. However, excessive exposure may result with respect to the background part in a range, which cannot be reached by the strobo light in the AE (automatic exposure control). Therefore, the background part may often be in a “defective white balance” state. For instance, when the face of a person M as the main foreground subject is picked up to be fairly good, a relatively remote scene as background has an observation factor corresponding to “defective white balance”, and even its profile is not clear.
Techniques concerning exposure control by the relation between amplifier gain and strobo light intensity have also been proposed (see Literature 1: Japanese Patent publication No. 3348799, for instance).
Again in such techniques, however, as stated in paragraph [0030] in the above literature, regarding the amplifier gain, either a “preset level” which has been preliminarily set is automatically increased, or the user presets the amplifier gain by manual operation, and the amplifier gain is not automatically preset to a proper gain corresponding to the exposure level of a background part which is not reached by strobo light.
As described above, no camera has been provided at present, in which when calculating the proper exposure by obtaining light reflected from the main foreground subject in the preliminary strobo light emission, a background part which is not reached by the strobo light is taken into consideration for photographing with proper exposure over the whole image.